1. Field of Invention
The present invention relates to the field of pollution control, and more particularly but not by way of limitation, to process apparatuses and methods for the disposal of noxious landfill-produced leachate, gases and condensate.
2. Discussion
Various kinds of wastes are buried in landfills that are known to produce noxious gases and condensates as the wastes decompose. In addition, water from rain and other sources percolates through the buried wastes, creating noxious leachates. These leachates are composed of a variety of chemicals, many of which are hazardous. Escaping gases and liquids from such landfills are recognized as sources of pollutants that present health and environmental hazards and must be collected and treated.
It is common to dispose of the noxious gases produced by a landfill by withdrawing these largely methane-based gases and burning them in flares or other types of gas combustion devices. In most cases removal of the noxious gases from the landfill results in the production of liquid condensates. These condensate liquids together with the leachate liquids have traditionally been collected and hauled from the landfill site for disposal. This process of disposal is of itself regulated and expensive as evidenced by the large amount of attention that has been given to the transportation and safe disposal of industrial waste liquids.
Prior art technology has been developed to deal with leachate and condensate disposal and includes the destruction of the liquid leachate in a gas-fired, direct contact evaporator, such as that taught in the patent to Young et al., U.S. Pat. No. 4,838,184. The Young patent teaches an apparatus and method for combusting a portion of the landfill gases and contacting a stream of the hot combustion products with the leachate liquids from the landfill to vaporize a portion of the leachate liquids. The composite gas stream is thereafter combusted. The Young process produces some particulate in the final combustion products which are exhausted to the atmosphere from the stack; furthermore, concentrated leachate residue is collected in the accumulator, and must be withdrawn and transported to an off-site location for appropriate disposal.
It is also known to treat leachate liquids and gases produced from landfills by diverting a portion of the combustion products, or flue gas, into an evaporator to concentrate the leachate liquid. This method also suffers from the drawback that the concentrated leachate must be hauled away for disposal. Both this process and that taught by the Young patent involve the use of wet sump pumps which, among other difficulties, present severe corrosion problems and thus potential operational unreliability.
These methods of dealing with leachate and condensate liquids suffer from another common drawback as a result of concentrating the leachate liquid. The Toxicity Characteristic (TC) of a leachate liquid stream is an expression of the concentration of certain EPA (Environmental Protection Agency) listed chemical compounds, such as chlorinated organics and heavy metals, among others. Once prohibited concentrations of such compounds are reached, as determined by EPA's Toxicity Characteristic Leaching Procedures (TCLP), the leachate stream becomes a hazardous waste which requires special processing. Anytime the liquid leachate is subjected to a concentrating process such as in the Young patent, there is a possibility that the liquid leachate may become so concentrated as to exceed the range of acceptable TC levels, requiring hazardous waste treatment. Clearly, such hazardous waste designation is undesirable.
In the past, one other approach provided for the direct injection of the landfill-produced leachate into a combustor. However, direct injection of leachate and/or condensate liquid into a landfill gas combustor is unlawful without appropriate regulatory permits, as direct injection changes the landfill gas combustor to a liquid incinerator, and more rigorous regulations apply to incinerators. The increased regulations are in large part due to the extreme variability in the composition of landfill-produced leachate liquid streams. The composition of the leachate liquid streams depends upon many factors, such as leachate flows and strengths, landfill age, and other environmental influences. For instance, as a landfill ages, many complex, non-biodegradable compounds are produced, often including chlorinated organics and heavy metals, among others. Landfill gas combustors are only permitted to burn gaseous fuels because such compounds found in leachate liquids often produce environmentally hazardous discharges. Another reason that landfill-produced leachate and condensate liquids cannot be burned in a landfill gas combustor is that any solids contained in the landfill-produced leachate or condensate liquids are exhausted from the combustion stack with the flue gas, presenting a potentially hazardous discharge of heavy metals or particulates in violation of regulatory requirements.
The direct injection approach also presents the possibility of a leachate spill should an injector become fouled of damaged. As is known, typical combustion equipment used for the destructive combustion of pollutants generally utilize ceramic fibers in the flame chamber for thermal protection of the metal components. Leachate spills can potentially damage ceramic fibers and, therefore, ceramic fibers are not recommended for use in furnaces which process liquids.
It would be desirable to have a disposal system that would overcome these and other limitations of the prior art systems. That is, it is desirable to have a disposal system which can lawfully dispose of all leachate, gases and condensates produced from any landfill of any age in an apparatus which disposes of such landfill pollutants on-site while producing combustion products which can be readily discharged in compliance with air quality standard and regulatory permits governing landfill gas combustors.